Jaydene Parsons, 23, and Karl Demetrius, 29, have admitted the charge but insist they did not know what was inside the bags hidden in the shed at their home.

Prosecutor William Mousley QC told the jury: "She was suffocated, despite her fighting for her life.

"There followed a deliberate, carefully planned and grotesquely executed plan to cover up her killing.

"Following her removal from her home, over the course of the next few days, her body was cut up with a knife and a power saw, the parts carefully packaged and then moved to another address to prevent them being found and lawfully buried, where they were intended to be stored probably temporarily until a final solution could be found."

Mr Mousley said the couple planned to kidnap Becky and had brought a stun gun, handcuffs, tape and a large bag to her home.

"In addition to their apparent dislike of Becky, there is good reason to believe there was also a sexual motive behind the scheme, arising from a shared unnatural interest in attractive teenage females, and that a foreseeable conclusion to it being carried out would either be Becky's death or serious injury," he added.

Members of Becky's family, who sat in the public gallery of court room two, left the court in tears during parts of the proceedings.

Becky was alone at the home she shared with her father Darren Galsworthy and step-mother Anjie - Matthews' mother - on February 19.

Matthews and Hoare, who had been in a relationship for six years, arranged for a key to be left outside the property so they could let themselves in.

It is not known exactly what time Becky was killed but she sent her final text to a friend at 11.03am.

The couple remained at the house - with Becky's body in their boot - for a further eight hours before driving home.

They ordered a Chinese takeaway before using their phones to browse for television programmes and order a pizza.

Becky's father reported her missing the following day and police launched an investigation.

Over the following days, Matthews and Hoare were captured on CCTV shopping for items including black bags, rubble sacks, rubber gloves and three rolls of clingfilm.

Mr Mousley said the couple spent three days completing "the lengthy process of cutting up and carefully packaging each individual parcel" and cleaning the aftermath.

Both Matthews and Hoare are accused of repeatedly lying to police by claiming they had heard a front door slam and Becky leave her home on February 19.

They were arrested on suspicion of kidnap and subsequently murder after Matthews' fingerprints were found on Becky's blood on door frames there.

During police interview on March 2, Matthews told police he had planned to kidnap Becky to "scare her and teach her a lesson because she was selfish and treated his mother badly", Mr Mousley said.

After a short struggle, he suffocated her and put her body in the boot of his car, driving home and unloading her corpse after Hoare was asleep.

He placed Becky's body in their bath and dismembered it using a circular saw, then hid the body parts downstairs.

These were placed in bags, suitcases and a box before being moved in to a shed at Barton Court - the home address of Parsons and Demetrius - in the early hours of February 24.

Police went to the property following Matthews' confession in interview and discovered Becky's body parts stored in the shed.

The circular saw, clingfilm, tape, female clothing, screwdrivers, scissors, gloves and face masks, a knife, bleach spray, an iPhone and a laptop were recovered from the shed.

Matthews' and Hoare's DNA was recovered on facemasks.

A post mortem examination found Becky was dismembered across her neck and above her knees, elbows and wrists.

Mr Mousley said police found a video clip on a phone belonging to Hoare and Matthews showing the rape of a teenage girl, with her attacker holding a hand over her mouth.

"Facebook dialogue between November and December 2014 found on a phone which was recovered show a shared interest in teenage girls, perhaps younger, and of kidnapping one of them," he said.

In 2013, Becky had told a friend she was scared of Matthews and he had "graphically" described how he would kill her.

The trial, expected to last for six weeks, continues.

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